What causes of action and remedies are available to Patrick in this situation?

Andrew McMillan is 70 years old and lives in an aged care home in Sydney. He owns a house in Armidale NSW, which has been on rent until a few years ago. Andrew finds it hard to manage the property in his old age and wishes to sell it.

Andrew’s nephew, Patrick McMillan, lives is Armidale and is a property developer. Although Andrew and Patrick were never close, Andrew can think of no one better than Patrick to offer to sell his property.

Andrew writes a letter to Patrick, which reads:
Dear Patrick,
It’s been a long time. Hope you are doing well. You know that I own the property at 7 Bound Street Armidale. I wish to sell it, and I thought that I should first offer it to you. If you would like to buy it, I am ready to sell it for $200,000.
Andrew

Unknown to Andrew the market price of the house is $220,000. Further, Andrew is unaware of the fact that the house can still fetch him good rental income.

In order to cash in on the opportunity Patrick accepts the offer straight away by a letter, which reads:
Dear Andrew,
I accept your offer. However, I will be able to pay you in 20 monthly instalments of $10,000. If this arrangement suits you send me your bank account details.
Patrick

Andrew writes back to Patrick. He agrees with arrangement and gives his bank account details.

Although Andrew mentions his return address on envelopes of his letters, Patrick fails to do so. Further, neither of the parties mention their full names on their letters.

Patrick gets the keys for the property made from a locksmith and takes possession of the property. He pays the first instalment to Andrew. He plans to put the house on rent after renovating it quickly and to continue paying the instalments to Andrew with the help of rental income from the house.

Patrick borrows $100,000 as a secured loan from a commercial bank and starts renovating the property. He does the landscaping of the garden, which has not been looked after for a few years. He is about to complete the renovation of the bathroom. He has also started getting the house repainted. Patrick has already spent $35,000 in the process, when Andrew comes to know about the real value of his property.

Andrew contacts Patrick and expresses his unwillingness to continue with the deal.

first one is valied with addresses
Second one not, incomplete?
Contract doesn't allow 10k deposits